Interaction of non-allelic genes
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The interaction of non-allelic genes
By Gunay Valizadeh
Azerbaijan Medical University
Faculty of Dentistry
Group: 421A-7b
INTRO
Non-allelic genes
Non-allelic are those genes that are localized indifferent areas of non-homologous chromosomes. Synthesis function they have one, but they code the formation of various proteins, causing different signs. Such genes, reacting with each other, can cause the development of symptoms in several combinations:
Combinations:
One sign will be due to the interaction of several, completely different in structure of genes.
A few symptoms will depend on one gene.
The reactions between these genes proceed somewhat more complicatedly than in the case of allelic interaction. However, each of these types of reactions has its own features and peculiarities
One sign will be due to the interaction of several, completely different in structure of genes.
A few symptoms will depend on one gene.
The reactions between these genes proceed somewhat more complicatedly than in the case of allelic interaction. However, each of these types of reactions has its own features and peculiarities
What are the types of interaction of non-allelic genes?
The types:
Epistasis.
Polymerism.
Complementarity.
The action of modifying genes.
Pleiotropic interaction.
Epistasis
This interaction of non-allelic genes is an epistasis- is observed in the case when one gene suppresses the activity of the other (the suppressing gene is called epistatic, and the suppressed gene is called the hypostatic gene).
The reaction between these genes can bedominant and recessive. Dominant epistasis is observed when the epistatic gene (usually it is designated by the letter I, if it does not have an external, phenotypic manifestation) suppresses the hypostatic gene (it is usually designated B or b). Recessive epistasis is observed when the recessive allele of the epistatic gene inhibits the manifestation of any of the alleles of the hypostatics of the gene.
example
Splitting by phenotypic trait, witheach of the types of these interactions, is also different. With dominant epistasis, the following pattern is more often observed: in the second generation the phenotypes will be divided into the following: 13: 3, 7: 6: 3 or 12: 3: 1. It all depends on which genes converge.
Complementarity
Complementarity
The interaction of non-allelic genes, in which a new phenotype, which has not been met before, is formed when a combination of dominant alleles of several characters is formed, and is called complementarity.
For example, most often this type of reaction between genes occurs in plants (especially in pumpkins).
If there is a dominant allele A or B in the plant genotype, the vegetable gets a spherical shape. If the genotype is reciprocal, the shape of the fetus is usually elongated.
If there are twodominant alleles (A and B) the pumpkin acquires a disk-like shape. If we continue to cross (ie continue this interaction of non-allelic genes with pumpkins of a clean line), then in the second generation it is possible to get 9 individuals with a discoid shape, 6 - with a spherical and one pumpkin of an elongated shape.
Such crossing allows to obtain new, hybrid forms of plants with unique properties.
In humans, this type of interaction causes the normal development of hearing (one gene is the development of the cochlea, the other is the auditory nerve), and in the presence of only one dominant trait, deafness is manifested.
Polymerism
Often the basis for the manifestation of a sign is not the presence of a dominant or recessive allele of the gene, but their number. The interaction of non-allelic genes - the polymer - is an example of such a manifestation.
The polymeric action of genes can proceed fromaccumulative (cumulative) effect or without it. With cumulation, the degree of manifestation of a sign depends on the overall gene interaction (the more genes, the stronger the sign is expressed). The offspring with this effect is divided as follows: 1: 4: 6: 4: 1 (the degree of the sign is reduced, ie, in one specimen the sign is maximally expressed; in others, its extinction is observed until complete disappearance).
If no cumulative effect is observed, thenThe manifestation of the sign depends on the dominant alleles. If there is at least one such allele, the symptom will take place. With this effect, splitting in the progeny proceeds in a ratio of 15: 1
The interaction of non-allelic genes, controlled by the action of modifiers, is relatively rare. An example of such an interaction is as follows:
For example, there is a gene D responsible forintensity of color. In the dominant state, this gene regulates the appearance of color, while in the formation of a recurrent genotype for a given gene, even if there are other genes that control directly the color, a "color dilution effect" will appear, as is often observed in milky white mice
Another example of such a reaction isappearance of spotting on the body of animals. For example, there is a gene F, the main function of which is uniformity of dyeing of wool. When a recessive genotype is formed, the wool will be colored unevenly, with the appearance, for example, of white spots in one or another area of the body.
Action of modifier genes
Pleiotropy
Pleiotropy
In this type of interaction, one gene regulates the manifestation or affects the degree of expression of another gene.
In animals, pleiotropy was manifested as follows:
In mice, the example of pleiotropy isdwarfism. It was noted that when mating phenotypically normal mice in the first generation, all mice turned out to be dwarfish. It was concluded that dwarfism is caused by a recessive gene. Recessive homozygotes ceased to grow, and their internal organs and glands were underdeveloped. This dwarfism gene influenced the development of the pituitary gland in mice, which led to a decrease in the synthesis of hormones and caused all the consequences.
Platinum color in foxes. Pleiotropia in this case was manifested by a lethal gene, which during the formation of a dominant homozygote caused the death of embryos.
In humans pleiotropic interaction is shown on the example of phenylketonuria, as well as Marfan syndrome.
Expressivity:
Expressivity:
A trait though penetrant, may be quite variable in its phenotypic expression, e.g., in human polydactylous condition may be penetrant in left hand but not in the right.
Penetrance
The ability of a gene to be expressed phenotypically to any degree is called penetrance. Penetrance may be complete, e.g., in pea, expression of R allele for red flower in homozygous and heterozygous conditions. It may be incomplete, e.g., dominant gene P for Polydactyly in human, sometimes does not show polydactylous condition in heterozygous state.